During the past years, interest in developing new oil and gas production fields has dramatically increased. However, the availability of land-based production fields is limited. Thus, the industry has now extended drilling to offshore locations, which appear to hold a vast amount of fossil fuel. Drilling is a complicated process that requires knowledge of pressures and temperatures (and other parameters) at the bottom of a well.
There are two types of situations when the pressures and temperatures of a well need to be monitored. The first situation is when the well is still being drilled, i.e., there is a drill line that runs through the well, and there is a drill bit at the end of the drill line for extending the well. In this case, as disclosed for example in U.S. patent application Ser. No. 12/363,092, the entire content of which is incorporated herein by reference, there is a continuous column of mud flowing from the drill bit to the surface of the rig. Using this continuous column of mud, a method of mud pulse telemetry data modulation (e.g., acoustic waves that propagate through the column) may be used to transmit information between sensors and computers located on the rig and various sensors (gauges) located in the well.
A second situation appears when the well is in the production phase, i.e., the drilling has been concluded and the well is used to extract oil and/or gas. For this phase, in order to know what is happening with the well, i.e., is there enough pressure to bring the oil or gas to the surface, etc., a monitoring system may be installed down the well. Such a monitoring system may be a downhole pressure and temperature gauge system. Other types of monitoring systems may be used that monitor more or fewer parameters of the well.
A downhole pressure and temperature gauge system in the well may provide its operator with real-time data and knowledge from the reservoir, and actions can be taken to improve reservoir drainage, lift performance, etc. When such changes are performed, the downhole sensing system verifies that the action decided by the operator has the required effect on the reservoir drainage. Thus, downhole sensing is advantageous for increasing drainage from the reservoir and saving costs by not having to perform downhole intervention surveys.
In other words, the gauge systems provide the operator with improved reservoir management, leading to increased daily production and increased total field drainage, better reservoir characterization, improved production optimization, better flow allocation and a real-time tool for well diagnostics.
However, there is a problem when the well is not active (a well is not active for various reasons) because a valve (e.g., downhole safety valve or other valves) in the well is closed and thus, there is no continuous column of fluid from the bottom of the well to the rig or Christmas tree. In this situation, the above-noted solution of using mud pulse telemetry might not work. Some existing solutions use, for example, a modified testing valve, and the pressure and temperatures can be read by an electric line device with communication based on an inductive coupling. Another solution is to use electromagnetic waves in a wireless manner or to use acoustic waves that are repeated up to the surface by plural repeaters for transmitting the information from the well to the surface.
The drawbacks of these existing solutions are that their implementations are cumbersome and not that reliable. The wireless solution highly depends on underground resistivity and seems not to work offshore. Alternatively, the use of modified testing tools or repeaters imposes a complex completion and requires highly-trained operators. In addition, the implementation of these solutions is costly.